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Reverse osmosis is a remarkably simple process of purifying
water and is well-suited for use in RVs. As the name implies, RO
reverses the natural process of osmosis, which is a very important
process utilized by living organisms.
What Is This Osmosis That You're Reversing?
Osmosis is the process of water molecules moving through
certain kinds of membranes, called "semi-permeable". If a
semi-permeable membrane separates two portions of water, one with
pure and one with tap water, then osmosis will occur. The water
molecules from the pure water side of the membrane will move
through the membrane and dilute the tap water. This is a
natural process that does not require any energy to make it work.
Why Would I Want To Reverse
Osmosis?
 Well, if osmosis is water molecules moving through a
membrane from the pure side to the tap water side, then reversing the process causes tap water to produce pure water. In RO, water molecules are
forced, with the help of some external energy, to move from a
"concentrated" solution (the feed water) through a semi-permeable
membrane. And, in an RO system, there is nothing on the other side
of the membrane to dissolve in the water, so you end up with pure
water. The energy that drives this process is the pressure that
the feed water is under.
Does RO Purify All The Water?
No. Under the best of conditions, including the right
membrane and adequate water pressure, about 20 to 30% of the water put
into an RO unit will come out as pure water. The rest is called
"brine" because it has a higher concentration of contaminants than
when it went into the unit. The brine performs the vital function
of carrying the contaminants away from the membrane, and it must
be disposed of in some manner.
Is The Purified Water 100% Pure?
No. RO does not remove all of the dissolved material from
the feed water. Some of the dissolved stuff will pass through an
RO membrane, thereby contaminating the "pure" water. The
amount that gets through is very small, somewhere between 2 to 20%
depending on the age and condition of the membrane. Generally, very few harmful contaminants
can pass through
an RO membrane. All sediment and most minerals will be removed by RO.
So What Are The Advantages of Reverse Osmosis?
RO can give you all of these benefits:
-
Delicious, pure, salt-free drinking water
-
Crystal-clear, pure ice cubes
-
Peace of mind, knowing your water is highly
pure
-
Compact, simple equipment - nothing to break
down
-
Cheap to operate - only requires water
pressure
If you use RO for all of your water, you'll get these
additional benefits:
How Much Water Will You
Process With RO?
Reverse osmosis produces highly purified water that is low
in minerals and
salts. As such, it functions as filter, purifier, and water
softener combined
into one system. Because of this, more and more RVers are
processing all of the water they use with RO. Many others
use RO only to purify their potable water for drinking and
cooking, and some want a small countertop unit to process just
their drinking water. Whatever size system you want, be
aware that RO is inherently a low-flow process, so you need to
consider some additional factors before deciding which
system will best fit your needs.
Water Pressure for RO: The More The Better
RO requires pressure to force water through a membrane, and
the more pressure you have, the better the system will work. You
need 40 psi of pressure as an absolute minimum for RO to even
work, and 60 psi or higher will enable the RO system to produce
pure water at a higher rate and of a higher quality. Also,
the membrane, which is the expensive heart of the system, will
last longer. If your pressure varies and often falls below
50 psi, we strongly recommend you use a booster pump to keep the
pressure to your RO system in the proper range.
Brine
Disposal: An Important Consideration
As discussed above, the brine produced in an RO system must
be disposed of. This is usually done by dumping it down the
drain. In some situations, this can be a problem for the
park's sewage treatment system, so you may need to use it to water
the lawn or other plants. The brine is not so concentrated
as to harm plants. If you will be using RO while dry
camping, water conservation is of utmost concern. In that
situation, you can always return the brine to your tank for use in
other ways.
Will An RO System Last Forever?
No. The membranes in RO systems eventually fail and need to be
replaced. There are two ways in which a membrane can fail, and you
can detect these failures easily. The first type of failure is
when the membrane gets plugged with contaminants, and it causes
the production rate of the system to drop off. The second type of
failure is a breakdown of the membrane itself. This is impossible
to see, and difficult to recognize. However, when this type of
failure occurs, the contaminants in the feed water will pass right
through the membrane. The only reliable way of detecting this type
of failure is to measure the Total Dissolved Solids (TDS) of your
product water on a regular basis with a
TDS meter. If you start to notice
an increase from your normal levels, then you probably have a
failed membrane that needs to be replaced.
Filtering Is Highly Recommended
As filtration devices, RO systems are subject to plugging
up, and the membranes are sensitive to chlorine. They will perform better and last longer if you pre-filter the
feed water to remove sediment and taste-and-odor contaminants.
This is best accomplished with a
canister system, either as a separate setup or as part of the
RO package. If you already have a filtration system in place, you
need only buy the Basic RO unit.
We also sell combination systems that include the
canisters and the RO unit as a package.
These systems include sediment and carbon filters.
Storage and Pressurization of the Pure Water
The pure water produced by the RO system must be stored for
later use,
and may need to be pressurized to make it convenient. How
these tasks are accomplished depends on the size of your system.
With a
countertop unit,
you supply a container that the unit fills with purified water.
Potable water systems are usually installed under your kitchen
sink and require a storage tank for the pure
 water.
We sell 2- and 3-gallon pressure tanks for
this purpose. Some pressure is developed by the RO system,
but for better pressure, we recommend you include a permeate pump
and/or a boost pump in your
system. If you want to use RO for all of your water, then
unless you have at least 50 to 60 psi of pressure, a boost pump
will be essential to provide adequate pressure to the membrane.
For a whole-RV system, you
will utilize your RV's water tank to store the pure water and the
built-in RV pump to deliver the water to your fixtures. You
will then be pumping the water out of your tank, acting like you
are dry camping, even though you are hooked up to a park's water
supply. In this situation, we
recommend you upgrade your original equipment pump with a
much-improved unit by Aquatec.
This improved pump will make your RV experience much more
enjoyable by providing quieter operation and higher flow and
pressure.
Controlling An RO System
Whenever you apply water pressure to an RO unit, it will
produce pure water, so the easiest way to start and stop one is to
turn a water valve on or off. For the countertop unit, this
is the only means of control you have. Our under-counter drinking
water system includes an automatic shutoff valve that senses
system pressure. For RO systems that are fed by a pump, we offer a control package
that can turn the system on and off when necessary to keep your
tank full without overflowing. There are many options
available to fit your specific needs.
A Word About Semi-Permeable Membranes
The semi-permeable membranes are the heart
 of
the reverse osmosis system, and they are typically installed in a
cylindrical housing that is similar to a filter canister. As with other filters, the material they
are made of makes a big difference in their performance and
longevity. We sell high-quality, thin-film membranes made by
Filmtec, a division of Dow Chemical. We have several sizes
available, with flow rates of 8 to 75 gallons per day. If the feed
water is pre-filtered to remove sediment and chlorine, the
membranes will last a long time. They do eventually
need to be replaced, so we sell replacement membrane units, and they
are easy to install.
To shop for RO systems and components that you can use to process
all of the water you use, go to
Whole RV RO Systems.
To shop for systems and components to provide RO on just your
potable water, go to
Drinking Water RO Systems.
Finally, if space is at a premium, and/or you just want a
small countertop RO unit, you'll find it in
RO Countertop Systems.
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